Frequency multiplier network



June 8, 1948. w. CARLSON ETAL 2,443,094

FREQUENCY MULTIPLIER NETWORK fined Dec. 18, 1946 /vo/v- LINEAR .2 TITANATE CONDENSER 1 OUT/Our INPUT 5 1 27 o-c VgLTAGE-(B) wlllugs u i Q Q 3. r :1 2 S b TEMPERATURE Q Q 14- -1-45? 645 I TEMPERAfURE emnskAu-(c) c, F 2 F 5 ES-E 5 (D) Q 20"% 4 Q 3 F 4 15- h 5 a (5) k E 10-; g 2 g '1 5- Q 2 i b 5' 1'0 1'5 26 2'5 3'0 is k PRIMARY VOLTS A T FUND. FREQ. Q 20 IF) U a I5, I O J Bummer-S. E9 Wendeil L. Caz-13012 t? I// 5 w 5 2o 2; so as APPLIED VOLTAGE Gflorueg Patented June 8, 1948 UNITED STATES PATENT. '0FFICE FREQUENCY MULTIPLIEB NETWORK Wendell L. Carlson and Hugh L. Donley, Princeton, N. J., assignors to Radio Corporation of America, a corporation of Delaware Application December 18, 1946, Serial No. 717,000

8 Claims. 1

tofore have utilized thermionic discharge detector tubes or crystal detectors connected in back-toback arrangement for generating harmonics of an applied fundamental frequency. All of such networks depend upon the non-linear resistance characteristics of the detectors employed, with resultant power loss in the frequency multiplier network. Another system employed heretofore utilizes a crystalline variable reactance element, such as a Rochelle salt crystal, for coupling together the fundamental frequency input circuit and the harmonic resonant output circuit. The disadvantage of'utilizing non-linear crystalline reactance elements is the difficulty of forming or obtaining suitable crystals, and the fragility and sensitivity to atmospheric conditions of such crystals.

The instant invention comprises improved methods of and means for generating and deriving integral multiples of an applied fundamental. frequency wherein a non-linear titanate ceramic ferro-electric device is utilized as a coupling element between a fundamental resonant frequency circuit and a harmonic resonant frequency circult. Since the reactance of the non-linear coupling element varies as a non-linear function of the applied unidirectional or alternating potential, the device may be operated under some conditions as a frequency multiplier having negligible power loss since the resistance is negligible and is not dependent upon the applied voltage within wide limits. It has been found that extremely small, thin, molded sections of barium-strontium titanate may be employed with a resultant high coupling coefiicient for an extremely small coupling device. Without a unidirectional bias voltage, the dielectric characteristics of the device will be substantially the same for both positive and negative alternating cycles, whereby odd integral harmonics will be generated. When a unidirectional bias voltage is applied to the device, even integral harmonics will be generated.

2 The non-linear titanate reactance elements have substantially a parabolic capacity vs. applied voltage characteristic (C(e)=Co+ae=). Thus, the charge q at any instant on the device 5 may be assumed to be where Cu is the capacity of the device, e is the excitation potential and K2 is a constant characteristic of the dielectric constant. Let

6: 13 E sin Wt+ E sin W 2 (2) where E0 is the unidirectional bias voltage applied to the condenser, E1 is the applied input signal voltage, and E2 is the applied local oscillator voltage in a superheterodyne network. Then Then The term (sin Wit cos Wit) in line 2 of Equation 5, when expanded, provides a frequency term cos 3W1t'which indicates that the device component in the impedance of the coupling device.

The terms (cos Wat sin Wit) and (sin Wat cos Wit) indicate that the sum and difference fre- 3 quencies of two applied signals may be derived. The coefllcients of these terms also indicate that the output of the device is proportional to the applied bias potential, the local oscillator voltage and the applied input signal voltage. A copending application of Hugh L. Donley and Chandler Wentworth Ser. No. 719,566, filed December 31, 1946, explains and claims the manner in which such a non-linear titanate reactor may be employed as a first detector in a superheterodyne receiver.

Another term cos Wat sin Wit sin Wat, in line of Equation 5, was expanded, gives /4 cos (W -2W2) cos (Wi-I-2W2). term indicates that the device will provide an output signal which corresponds to the beat frequency signal between the input signal and the second harmonic of the oscillator signal. This feature also is described and claimed in said copending application and provides an improved noise factor which is especially desirable at ultra high frequencies.

Experimental data indicate that there are optimum values for the magnitude of the unidirectional bias voltage to provide even integral harmonic generation. Also there are optimum limits of signal excitation for maximum efliciency of the device as a frequency multiplier or signal mixer. have non-linear temperature coefficients of dielectric constant. In samples of the material having approximatelyBO per cent barium titanate oxide and 20 percent strontium titanate oxide, the portion of the temperature coefficient characteristic occurring at room temperatures is entirely satisfactory for operation as a frequency multiplier or mixer. It should be understood, however, that other applications of the device may utilize the portions of the temperature coefficient characteristic having a zero or negative slope provided that suitable temperature control is provided.

Among theobjects of the invention are to provide improved methods of and means for generating and selecting multiples of substantially any applied fundamental frequency. Another object is to provide an improved frequency multiplier employing a non-linear reactance element as a coupling between tuned input and output circuits. A further object of the invention is to provide an improved frequency multiplier utilizing a titanate ceramic non-linear reactance element. improved frequency multiplier network comprising a tuned input circuit, excited at a fundamental frequency, coupled through a titanate ceramic non-linear capacitor to a tuned output circuit resonant to a predetermined harmonic of the applied fundamental frequency.

A further object of the invention is to provide an improved frequency multiplier network employing a non-linear reactance element and including means for applying a unidirectional bias potential to said element to limit the derived output signals to even integral harmonics of the applied signal. A still further object of the invention is to provide an improved frequency multiplier network utilizing a titanate ceramic capacitor having a non-linear temperature coemcient of. dielectric constant and a nonlinear capacity characteristic as a function of excitation voltage. An additional object of the invention is to provide an improved frequency multiplier network utilizing a non-linear titanate ceramic reactance element having a An additional object is to provide an 4 negligible resistive component and negligible power loss. Another object is to provide an extremely small, efficient, and economical frequency multiplying device.

The invention will be described in further detail by reference to the accompanying drawing of which Figure l is a schematic circuit diagram of This expanded Such non-linear titanate reactors also a preferred embodiment thereof, Figure 2 is a family of graphs illustrative of the relation between the capacity of non-linear titanate capacitors and applied A. C. or D. C. potentials, Figure 3 is a group of graphs showing the relation between the operating temperature and dielectric constant of titanate capacitor coupling elements, Figure 4 is a family of graphs illustrating the relation between applied fundamental frequency signal magnitudes and derived third harmonic signal magnitudes as well as the relation between said applied fundamental frequency signals and the input-to-output power ratio, and Figure 5 is a group of graphs illustrative of the power-factor of titanate capacitors as a function of applied signal magnitudes. Similar reference characters are applied to similar elements throughout the drawing.

Referring to Figure 1 of the drawing, an input circuit 3 comprising a parallel-tuned inductor 5 and capacitor 1 is resonant to a source of input signals, not shown, having a frequency f. The tuned input circuit 3 is coupled through a non.- linear titanate ceramic capacitive device 9 to a tuned output circuit ll comprising a parallelconnected second inductor l3 and second capacitor IS, the output circuit being resonant to a desired integral harmonic M of the input frequency j. The non-linear titanate coupling device 9 preferably comprises an extremely thin section I! (of the order of 1.5 mils) of bariumstrontium titanate having a diameter of the order of 5 mils. The use of a thicker dielectric requires higher excitation voltage. Capacitive electrodes I9, 2| are deposited upon, or coated upon, opposite surfaces of the titanate dielectric l1, and terminals are provided thereto for connection to the input and output tuned circuits 3 and II. It has been found that the proportions of percent barium-titanate oxide and 20 percent strontium-titanate oxide provide a satisfactory mixture for a low temperature coefiicient at room temperature. However, other proportions having different temperature coemcients as well as sensitivity factors may be employed.

Without a unidirectional bias voltage applied to the titanate coupling device, the dielectric characteristics thereof will .be substantially the same for both positive and negative portions of the alternating cycle, thereby providing odd integral harmonic generation. If only this type of harmonic generation is desired, the remaining terminals of the tuned input and output circuits may have a common ground connection.

However, if a unidirectional bias voltage is desired for the titanate coupling device in order to generate even integral harmonics of the input frequency a coupling capacitor 23 is connected between the low potential terminals of the input and output tuned circuits 3 and II. A source of bias voltage, such as a battery 25, and a potentiometer 21 is connected in parallel with the coupling capacitor 23, providing a continuously adjustable source of bias voltage for the titanatecoupling device. When the adjustable contact 29 of the potentiometer 21 is adjusted to provide a zero bias voltage, the coupling capacitor 23 is efiectively short circuited, and the low potential terminals of the input and output tuned circuits are effectively directly connected together for odd integral harmonic variation.

Figure 2 includes a first graph (A) characteristic of the variation of the capacity'of an 80 percent barium titanate oxide-20 percent strontium titanate oxide coupling unit as a function of an applied alternating potential. Graph (a) is characteristic of the variation of the capacity of a 69 percent barium titanate oxide-31 percent strontium titanate oxide coupling device as a function of the same applied potentials. Graph (B) is characteristic of the variation in capacity of the titanate coupling device as a function of an applied unidirectional voltage. Both graphs indicate the operation of the device at a temperature of 20 C.

Figure 3 shows a graph (G) characteristic of the variation of dielectric constant of an 80 percent barium titanate oxide-20 percent strontium titanate oxide coupling device 9 as a function of operating temperature in degrees C. Graph (0) shows the different characteristics for a 69 percent barium titanate oxide-31 percent strontium titanate oxide device. Comparison of the graphs (A) and (C) of Figures 2 and 3 indicate that the device may be operated as an extremely sensitive variable capacitive element as a function of an applied alternating potential while having simultaneously a relatively low temperature coeilicient of dielectric constant at an average room temperature of 20 C. Comparison of graphs (a) and (c) of Figures 2 and 3 shows that an element of reduced sensitivity to applied voltage may be operated at widely different portions of the temperature-coefficient characteristic which may be desirable from a power-factor standpoint, as will be seen from graphs (F) and (G) of Figure 5.

Figure 4 shows in graph (D) the secondary voltage at the third harmonic frequency 3/ as a function of input voltage at the fundamental frequency Graph (E) indicates the ratio of input to output power of the network at a harmonic frequency 11 as a function of input voltage at the fundamental frequency f. This ratio as illustrated is characteristic of the relation between input power at the fundamental frequency and output power for substantially any low harmonic frequency value, since the resistive component of the coupling device has a substantially negligible value. The coupling between the tuned input and output circuits 3 and H is substantially a higher order non-linear function of the variation in reactance of the coupling device which for practical purposes is purely reactive.

In Figure 5, graph (F) indicates the relation between power factor and applied signal magnitudes for a capacitor having a dielectric of 80 percent barium titanate oxide and 20 percent strontium titanate oxide. Graph (G) indicates the widely diflerent relation between power factor and applied signal magnitudes for a capacitor having a dielectric of 69 percent barium titainate oxide and 31 percent strontium titanate 0 de.

Thus the invention disclosed and claimed herein comprises an improved frequency multiplying network utilizing a non-linear titanate ceramic capacitor employing a barium strontium mixture for coupling together an input circuit tuned to a fundamental frequency and an output circuit tuned to a predetermined harmonic frequency. Means is included in the network for providing an adjustable unidirectional bias voltage for the coupling device in order to generate even integral harmonic frequencies. the advantages of extremely small size, negligible power loss, and extremely stable operating characteristics.

We claim as our invention:

1. A signal frequency multiplying device comprising a non-linear substantially reactive ceramic ferroelectrie device, means for applying signals to said device and means for deriving output signals from said device, the frequency of said output signals being an integral multiple of the frequency of said applied signals.

2. A signal frequency multiplying device according to claim 1 including means for applying a unidirectional bias potential to said ferro-electric device for limiting the frequencies of said output signals substantially to even integral multiples of said applied signal frequency.

3. A frequency multiplying network for a source of signals comprising an input circuit responsive to said signals, an output circuit tuned to an integral multiple of the frequency of said input signals, and a non-linear substantially reactive ceramic ferroelectric device coupling together said input and output circuits.

4. A frequency multiplying network for a source of signals comprising an input circuit tuned to and responsive to said signals, an output circuit tuned to an integral multiple of the frequency of said input signals, and a non-linear substantially reactive refractory ferroelectric device coupling together said input and output circuits.

5. A frequency multiplying network for a source of signals comprising an input circuit responsive to said signals, an output circuit tuned to an integral multiple of the frequency of said input signals, and a non-linear substantially reactive coupling device comprising a capacitor having a titanate ceramic dielectric, said device coupling together said input and output circuits.

6. A frequency multiplying network for a source of signals comprising an input circuit tuned to and responsive to said signals, an output circuit tuned to an integral multiple of the frequency of said input signals, and a non-linear substantially reactive coupling device comprising a capacitor having a barium-strontium-titanate dielectric, said device coupling together said input and output circuits.

'7. A frequency multiplying network for a source of signals comprising an input circuit tuned to and responsive to said signals, an output circuit tuned to an odd integral multiple of the frequency of said input signals, and a non-linear substantially reactive coupling device comprising a capacitor having a titanate refractory dielectric, said device coupling together said input and output circuits.

8. A frequency multiplying network for a source of signals comprising an input circuit tuned to and responsive to said signals, an output circuit tuned to an even integral multiple of the frequency of said input signals, a non-linear substantially reactive coupling device comprising a capacitor having a titanate dielectric, said device coupling together said input and output circuits, and means for applying a unidirectional bias potential to said device to provide said even multiple frequency multiplying characteristic.

WENDELL L CARI-SON. HUGH L. DONLEY.

The coupling device has, 

